1. Field of the Invention
The present invention relates to an optical add-drop multiplexer (OADM), and particularly to a re-configurable OADM.
2. Description of Related Art
Wavelength division multiplexing (WDM) is widely used in optical communication systems. There is a need to route one or more channels of a WDM signal to different destinations. Thus, an optical add-drop multiplexer (OADM) is introduced into the optical communication system to drop optical signals having desired wavelengths from an optical WDM signal and to add optical signals having the same wavelengths and carrying new information. The OADM also needs to be re-configurable to be flexibly accommodated in various applications.
U.S. Pat. No. 6,035,080 discloses a re-configurable OADM including a re-configurable add-drop unit that can add-drop one channel out of a large set by mechanically switching the light path through one of a set of fixed add-drop filters. Re-configuration is done by switching from the add-drop filter path to a bypass path, changing to a different add-drop filter, and then switching back. However, only one of the set of fixed add-drop filters can be used to add-drop one channel, so this re-configurable OADM is not cost-efficient. In addition, the number of channels which can be dropped by this re-configurable OADM is unchangeable.
Therefore, an improved re-configurable OADM is required to overcome the above problems.